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Abstract
Benthic microalgae inhabiting marine sediments, composed primarily of diatoms, are an important carbon source for a variety of meiofaunal and macrofaunal organisms. The purpose of our study was to determine if this benthic microalgal assemblage exhibits short-term (hourly) changes in the vertical distribution of biomass in the upper few mm of intertidal mudflat sediments in North Inlet estuary (South Carolina, U.S.A.). Sediment cores were collected and subsampled at 2 and 3 h intervals over 2 tidal cycles on 4 different dates to quantify changes in chlorophyll a concentrations at 1 mm intervals in the upper 3 or 5 mm of sediment. Benthic microalgal biomass showed significant changes in vertical distribution over time that were attributed to migration by motile benthic diatoms. Migration was limited primarily to the upper 3 mm of sediment with ca. 33% of the total biomass in the upper 1 mm undergoing migration. Comparisons with a microalgal production model, which was based on tide and sun variables, showed that predicted production was highly correlated with the microalgal biomass in the upper 1 mm of sediment. Vertical migration by benthic microalgae may therefore explain much of the observed short-term variability in primary production in marine sediments. Changes in the relative availability of benthic microalgae in the upper few mm of sediments may be of importance to the foraging strategies of surface deposit feeders.
